Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Stanislav Houzar, Milan Novák

Marbles with carbonatite-like geochemical signature from variegated units of the Bohemian Massif, Czech Republic, and their geological significance

Journal of the Czech Geological Society, volume 47 (2002), issue 3-4, 103 - 110

Marbles with carbonatite-like geochemical signature (MCC) were recently found at several localities of ordinary calcite marbles (OMC) in the Český Krumlov (Muckov), Vratěnín (Korolupy), Olešnice-Lamberk) and Vranov (Vranov) Units, respectively. The rock complexes hosting the MCC are built of dominant metapelites with locally common intercalations of quartzites, calcite and dolomite marbles, minor metabasites, graphite-rich rocks and locally scapolite- and tourmaline-bearing rocks (metaevaporites?). The mineral assemblages of the OMC and MCC are very similar and include Cal+Dol+Phl, Cal+Dol+Tr, Cal+Qtz+Phl+Na,Al-enriched amphibole (tremolite, fluortremolite, edenite, pargasite, magnesiohornblend), Cal+Dol+Tr+Di. Relatively abundant diopside in the Moldanubian marbles indicates a higher grade of metamorphism relative to the Moravicum. The MCC have variable contents of Si and Al from almost pure marbles to silicate-rich rocks with up to 31.7 wt.% SiO₂ and 4.49 wt.% Al₂O₃, high SiO₂/Al₂O₃ = 21.35-6.18 is typical. The associated OMC and MCC do not exhibit any apparent differences in the major elements, disregarding slightly lower SiO₂/Al₂O₃ ratio, slightly increased Na and K contents in the MCC, nevertheless, they are enriched in Nb ≤ 393, Mo ≤ 28, REE_total ≤ 124, Zr ≤ 4212 and Sr ≤ 1063 (all in ppm). The carbonatite-like geochemical signature may be caused by admixture of detritus from relatively primitive volcanic rocks or participation of the evaporitic fluids mobilized from host rocks. Presence of the MCC in lithologically similar metamorphosed volcanosedimentary sequences, currently classified into distinct geological units (Moldanubicum, Moravicum), indicates that they may represent an identical unit in the Bohemian Massif.